Cardiac action potentials can be recorded optically using the fluorescent emission of the voltagesensitive dye di-4-ANEPPS. A challenge in optical recording is the motion artifact that appears during the repolarization phase of the action potential. Uncoupling agents such as diacetyl monoxime (DAM) are used to inhibit mechanical contraction. These uncoupling agents can cloud the true electrophysiology of the tissue by changing action potential duration and the refractory period. In addition, the techniques commonly used for optical recording typically do not allow for recording below the epicardial surface. The proposed research is to use a fiber-based non-ratiometric system to document the motion artifact without the use of a mechanical uncoupling agent. After evaluation, a novel compact ratiometric channel will be designed to suppress the motion artifact. The device is based on the novel use of light emitting diode illumination, a diffraction grating, and a split photodetector. Finally, the measurement of action potential duration within the moving ardiac wall will be used to determine the ability of a ratiometric system to decrease the motion artifact without the use of a mechanical uncoupling agent. [unreadable] [unreadable]